BobQ

I need to R/R my evaporator and need a vacume pump to pull down the system, does anyone have a good recomendation for a good pump? I don't need a snap-on or anything that good, it will only get light use. I have also seen the phnumatic type, and have a cheap one from harbor frieght, but have heard they are not that effective? I don't want to get it all apart and have to hold up the job waiting for a good pump!

Thanks for any recomendations.

Bob

Sorry for the double post, I posted in the wrong area and did not know how to move it!

BC847

Regardless of the CFM claims be it 3 or 5 or what ever, get one that pulls to the deepest vacuum (microns). You'll need a proper micron guage to be able to read a vacuum that deep.

With that you'll be able to correctly and completely evacuate and dehydrate the refrigerant circuit.

Evacuation ~ this is where one removes all the non-condensible gasses such as air that got into the plumbing/system while it's apart.

Dehydration ~ this is where one removes any traces of moisture be it water, acid, or whatever that may have formed in the refrigerant circuit while it was running with an incorrect refrigerant charge (for example). Left un-addressed, said moisture can lead to formation of acids, sludge, etc that will shorten the life of the compressor as well as threaten plugging orifices, etc.
This is where a pump capable of VERY deep vacuum is necessary. As you may know, water boils at 212*F at sea level (14.7psia). If we drop that pressure on the water, the boiling point drops. Don't quote me, but at about 25 or so inches of mercury (unit of measure for a vacuum), water boils at about 75*F. With taking the vacuum even deeper (microns), one is assured all moisture is removed from the refrigerant circuit.
This is why one often sees references to running the vacuum pump for an hour or so. Those time figures are often the result of one NOT having a micron guage to properly see where one is at regarding how deep the vacuum is.
Therefore, having a good vacuum pump capable of pulling down to 100 microns combined with a micron gauge to see it, run the pump till you see the vacuum pull down to less than 1000 microns and close off the pump valve. Watch the micron guage to see where the vacuum goes to. If the vacuum rises to about 1500 microns and stops, you still have moisture in the circuit. Run the pump more. If you see the vacuum rise on up well above 1500 microns and it continues to rise, you have a leak. Stop and fix it.

You'll know positively of a good and proper vacuum if you can pull it down to less than 350 microns and not see it go above 1000 microns within ten minutes time.

I hope this helps more than confuses.

BE sure to use fresh vacuum pump oil.

BobQ

Thanks, not confused at all. I was wondering, do you need to drain out the old oil or does it come out from the leak? my system is empty so I don't need to evacuate it, I noticed a little plug at the bottom of the compressor and thought it may be for draining the old oil?

also how does this look for a pump?

http://www.tooltopia.com/index.asp?P...OD&ProdID=9013

Thanks Bob

BC847

Robinair is a well known brand. The specs say that pump's good for 20 microns though in real-life, perhaps 100. Anyhoot, it will work just fine.

Oil? Leak?

Fresh oil is needed in the VACUUM pump for it to be able to perform correctly vacuum wise.

Regarding the AC compressor oil, if you're gonna use the original type of refrigerant in the system, barring any problems with the original compressor, etc, don't change the oil.

Typically, any refrigerant leak will often visually present as an oily spot (some of the compressor oil moves about the refrigerant circuit and thus will leak out with the refrigerant). If you feel like you've lost, . . . say . . .. a tablespoon or so . . . don't worry with it.



You say the system is empty. I assume you mean empty of refrigerant. You still must evacuate the refrigerant circuit as pending where the leak was, the system can operate in a vacuum with a very low refrigerant charge and suck in air.

It's a moot point though. The only real difference in using the vacuum pump regarding an Evacuation or Dehydration is the TIME the pump is run. The dehydration will take longer IF there's moisture present and then how much. In the end, the micron guage will tell you accurately when you're done.


Be sure to include replacing the receiver tank as it has a sack of a chemical desiccant drier built in. It will help ensure a long lived system.

BC847

I've edited the post above . . . . a couple of times now. Sorry.

I've got to go fix Uncle Bobby's porch light. I'll check back here shortly.

BobQ

Thanks! Very helpfull! I was refering to the oil in the ac system, my evaporator has been leaking for about a year and a half, just getting around to doing it now, I was not sure if the oil was a gas or liquid, if that makes sence? I alway see oil at the leaks (on other systems) so figured maybe it all comes out?

I will order the pump, there is one a little bigger, I will order that one instead, I think 6cfm.

I need to do my vp44 first, it is in the mail.

Bob

BC847

The refrigerant oil does intimately mix with the refrigerant while it's in a liquid state. The normal operation of the compressor will pick up a little oil from the compressor's crankcase by the refrigerant, crankshaft or wobble-plate, . . .kicking around in there. It will carry through the compressor and become mixed with the liquid refrigerant. Once in the evaporator, the refrigerant will boil off leaving a notable amount of oil in the evaporator. The velocity of the now gaseous refrigerant will carry the oil back to the compressor (with the properly sized plumbing.

The only real advantage of a larger CFM rated vacuum pump is it will pump a circuit down to approx 0psig quicker. It's helpful when working on larger systems. It's also heavier so keep that in mind if you have to haul the blame thing up a ladder a lot.

BobQ

Great, thanks for the help, what about recovery of the old refrigerant? the system has been down for over a year and a half, should I pay someone to recover what may be left in the system? it seams once you go that far they want to do the repair, or explain to you why you are too dumb to do it your self, and how every thing you miss, and you will, will cost you millions in the end.

Thanks Bob

BC847

The typical automobile system doesn't hold a lot when fully charged. If it's low enough that the system doesn't run the compressor, there's most likely not enough refrigerant left to warrant connecting the hoses.

Things happen if you know what I mean (you never SAW me say that).

BobQ

Ya, I know what you meen, I like to be green, but the comp will not come on at all, no sence burning up fuel for nothing.

Also, what type of oil is in the system? it is a 2001? I want to lube the new O-rings for install.

Also, is oil lost when replacing the dryer canister? I plan on replacing the dryer and evaporator. Can you over fill the oil?

Bob

Jim Lane

This the vacuum pump that I am using, I have 2 of these Edwards E2M2 Rotary Vane Mechanical pumps that I had bought from a surplus dealer that sell interesting things like wave guides, attenuators, dewars and laser storage capacitors. (I was in pig heaven in that place)

I ask the wife that was there how much? And she did not know what they were so she finally said $50.00 each for the motors, and I said well OK.

One was new still in the box and the other one had been used but they both had a tag
Certified to 3 microns tied to the handle.

Supposedly they are for a Scanning Electron Beam Microscope.

All that I had to do was purchase a different inlet fitting and add a power cord.
It is also light enough to carry up a ladder 2 stories onto the roof whenever I leave it unattended it is locked down with a cable and padlock.
Jim

http://www.pchemlabs.com/static/pid=1069.html